If you want popular bloggers to join or write about your community, cram as much value into your invite as you possibly can
1) Explain you want them because they’re experts who would add value to your community.
2) Ask if they would like to have first-look, product review opportunities. Perhaps attend one of your client’s events.
3) Mention you’ve already reserved their username and password for them. No-one else can take it, all they need to do is log-on.
4) Offer them a position of responsibility/expertise in your community. Maybe a group/forum/page just for their readers?
5) Ask for advice on making the community better.
6) Mention whether they join or not you would like to send a trial/sample of your product for them to enjoy.
7) Name drop their friends and rivals who have joined. Better, get their friends/rivals to invite them to join.
8) Offer a community badge featuring their name as a VIP member of your community which they can display on their blog/facebook.
9) Once they’ve joined you would like to interview them for the community website.
10) Explain you only have 10 of these super-invites and they can decide which other bloggers in their field get them.
But try to keep the it short.